Eventually, all galaxies, including our own Milky Way, will reach their end.
But how do galaxies die? If you’re in the mood to destroy an entire galaxy, you have a few options depending on the level of destruction you want.
Related: Monster black holes may have murdered their host galaxies in the early universe
Option 1: Awaken the black hole monster
At the heart of almost every galaxy is a supermassive black hole. In the case of the Milky Way, we have A* scorer, a beast weighing more than 4.5 million suns. Usually these giant black holes are quiet and dormant, just gobbling up any bits of gas or stars that wander too close. But sometimes they enjoy a much larger meal. When they do, this gas swirls and compresses around them, reaching temperatures well over a billion degrees.
These ridiculously high temperatures cause the gas to emit massive amounts of radiation, which then flood the whole galaxy, heats up all the gas reserves and prevents the formation of new stars. Even if everything usually calms down after that, in the worst cases radiation from the surroundings Black hole it can completely eject huge amounts of gas from the galaxy.
It won’t completely destroy the galaxy, but it will effectively kill it by preventing new stars from forming for a very long time, and in some cases forever.
Option 2: Place it in a cluster
Galaxy clusters are the dense urban centers of the universe, usually home to a thousand or more galaxies. But these clusters contain more than just galaxies; they also contain vast reservoirs of hot, rarefied gas known as the intracluster medium (ICM).
The ICM is so thin that it would register as a vacuum in laboratories on Earth. But when galaxies fall into a cluster, they still have to navigate through it. Initially, this leads to a short round of star formation as shock waves compress gas clouds throughout the galaxy. But eventually the pressure of the gas does its job, picking up chunks of gas from the galaxy like debris flying off a meteorite.
This leads to a cute situation known as “jellyfish galaxy,” so called because the exposed gas resembles the tentacles of a jellyfish. Although most galaxies survive their descent into the ICM cluster, some smaller galaxies evaporate completely.
Option 3: Crash into another galaxy
Galaxy collisions represent one of the largest releases of energy in the known universe, and that means it’s not exactly a pretty sight. Our own Milky Way will collide with our neighbor’s the Andromeda Galaxy in about 5 billion years.
A slow and painful process taking hundreds of millions of years, galaxy mergers can give rise to huge tidal tails, which consist of streams of broken-off stars and gas that arc around galaxies. Countless stars are lost during collisions and mergers with random interactions. And once the respective supermassive black holes meet, a new round of radiation hits the newly merged galaxy. The combined devastation will deplete the galaxy’s supply of gas, stopping star formation for good.
Option 4: Feed it a much larger galaxy
If a smaller galaxy and a much larger companion merge, it could spell the end of the smaller galaxy. After all, the European Space Agency Gaia exploration found the bones and corpses of cannibalized galaxies littered throughout the Milky Way.
One such example is known as Gaia sausage. This collection of stars scattered around the Milky Way’s core share properties such as abundances of heavy elements and orbital parameters that differ from the rest of the population. Astronomers believe that the stars in the Gaia sausage are the tattered remains of a small dwarf galaxy that was torn apart by its merger with the larger Milky Way.
Astronomers have identified dozens of other such collections, streams, clumps and remnants – a sign of the violent merger history of any decent-sized galaxy like ours.
Option 5: Wait
Time will eventually take its toll. Galaxies are remarkably stable; many of them have been around for over 10 billion years. But nothing lasts forever.
Far, far in the future, when the universe is many times older than today, the Milky Way-Andromeda merged galaxy begins to dissolve. It is simply a matter of gravitational coincidence. Most stars spend most of their lives nowhere near each other, but occasionally they wander too close. When they do, they perform a little gravity dance that sends them off in new directions. Very rarely can a person gain enough energy to escape the galaxy completely.
This is incredibly rare, but after trillions and trillions of years it is bound to happen. Eventually, everything in our galaxy will either end up in a giant black hole or be dispersed into the wider universe. And that will truly be the end of our galaxy.